laser

#### FILTER

Pointcloud Operator dialog box - FILTER Operator

The FILTER operation filters data to a smaller subset of points.

To apply the FILTER operation to a pointcloud, click Filter Pointcloud () on the Pointcloud toolbar, or select Operation | Pointcloud | Filter.

The FILTER operator uses the following options:

Type - Indicates the type of filter operator to apply: UNIFORM, CURVATURE, RANDOM, DISTANCE, or INCIDENCE ANGLE.

UNIFORM - Generates a subset of points distributed evenly in the X, Y, and Z directions. It produces the same effect as a regular grid in 2D, but in this case the effect is a 3D grid.

CURVATURE - Generates a subset of points with the highest estimated curvatures, mainly around edges, vertices, and highly curved areas of the surface.

RANDOM - Generates a subset of points randomly distributed in the pointcloud.

DISTANCE - Generates a subset of points where points are at least the specified Distance value apart from each other.

Distance - When DISTANCE is selected, the value entered specifies the distance for the distance filter.

INCIDENCE ANGLE - Generates a subset of points which excludes (i.e., filters out) points that have a normal vector orientation that fall outside the specified angle, relative to the laser sensor orientation. This filter allows you to remove laser points caused by secondary reflections or "noise". You can see the effect of this filter after you click the Apply button in the dialog box.

A valid value is any real number from 10 to 90, inclusive.

To use this filter, the pointcloud data must have vector information.

To filter COP data:

1. From the Type list, select a filter type .

2. From the list of commands, select the Pointcloud command to which you want to apply the filter.

3. Specify the number of points or percentage of points to keep after applying the filter in the Reduced or % boxes. This does not apply to the Distance filter.

4. Click the Apply button.

PC-DMIS filters the data, and the Graphic Display window shows the result. The size of the filtered data may differ slightly from the value that you specified. It is even more noticeable when the measurement routine is executed and the data is collected from scan commands. It is generally impossible to get the same number of points from a laser sensor that is repeatedly scanning the same entity.

5. When you are satisfied with the result, click the Create button. PC-DMIS adds a COPFILTER command to the measurement routine containing all the information regarding the filter that you just applied.

Click Create to insert a COP/OPER,FILTER command into the Edit window like the following examples:

COPFILTER3=COP/OPER,FILTER,UNIFORM,SIZE=3000

REF,COP1,,

In the example above, if the initial size of COP1 was 10,000 points, the filter replaces the 10,000 points held in COP1 with the filtered 3,000 points, so that COP1 now holds the filtered 3,000 points for its cloud of points. PC-DMIS flags the 7000 points it didn’t use, so that you can undo the filter operation, using the RESET operation. Or if you desire, you can permanently purge the 7000 points not used using the PURGE operation. For more information, see "RESET" and "PURGE".